1 | =head1 NAME
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2 |
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3 | perlfaq1 - General Questions About Perl ($Revision: 1.19 $, $Date: 2005/12/31 00:54:37 $)
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4 |
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5 | =head1 DESCRIPTION
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6 |
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7 | This section of the FAQ answers very general, high-level questions
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8 | about Perl.
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9 |
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10 | =head2 What is Perl?
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11 |
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12 | Perl is a high-level programming language with an eclectic heritage
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13 | written by Larry Wall and a cast of thousands. It derives from the
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14 | ubiquitous C programming language and to a lesser extent from sed,
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15 | awk, the Unix shell, and at least a dozen other tools and languages.
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16 | Perl's process, file, and text manipulation facilities make it
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17 | particularly well-suited for tasks involving quick prototyping, system
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18 | utilities, software tools, system management tasks, database access,
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19 | graphical programming, networking, and world wide web programming.
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20 | These strengths make it especially popular with system administrators
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21 | and CGI script authors, but mathematicians, geneticists, journalists,
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22 | and even managers also use Perl. Maybe you should, too.
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23 |
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24 | =head2 Who supports Perl? Who develops it? Why is it free?
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25 |
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26 | The original culture of the pre-populist Internet and the deeply-held
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27 | beliefs of Perl's author, Larry Wall, gave rise to the free and open
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28 | distribution policy of perl. Perl is supported by its users. The
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29 | core, the standard Perl library, the optional modules, and the
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30 | documentation you're reading now were all written by volunteers. See
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31 | the personal note at the end of the README file in the perl source
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32 | distribution for more details. See L<perlhist> (new as of 5.005)
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33 | for Perl's milestone releases.
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34 |
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35 | In particular, the core development team (known as the Perl Porters)
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36 | are a rag-tag band of highly altruistic individuals committed to
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37 | producing better software for free than you could hope to purchase for
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38 | money. You may snoop on pending developments via the archives at
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39 | http://www.xray.mpe.mpg.de/mailing-lists/perl5-porters/
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40 | and http://archive.develooper.com/[email protected]/
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41 | or the news gateway nntp://nntp.perl.org/perl.perl5.porters or
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42 | its web interface at http://nntp.perl.org/group/perl.perl5.porters ,
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43 | or read the faq at http://simon-cozens.org/writings/p5p-faq ,
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44 | or you can subscribe to the mailing list by sending
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45 | [email protected] a subscription request
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46 | (an empty message with no subject is fine).
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47 |
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48 | While the GNU project includes Perl in its distributions, there's no
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49 | such thing as "GNU Perl". Perl is not produced nor maintained by the
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50 | Free Software Foundation. Perl's licensing terms are also more open
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51 | than GNU software's tend to be.
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52 |
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53 | You can get commercial support of Perl if you wish, although for most
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54 | users the informal support will more than suffice. See the answer to
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55 | "Where can I buy a commercial version of perl?" for more information.
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56 |
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57 | =head2 Which version of Perl should I use?
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58 |
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59 | (contributed by brian d foy)
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60 |
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61 | There is often a matter of opinion and taste, and there isn't any
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62 | one answer that fits anyone. In general, you want to use either
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63 | the current stable release, or the stable release immediately prior
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64 | to that one. Currently, those are perl5.8.x and perl5.6.x, respectively.
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65 |
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66 | Beyond that, you have to consider several things and decide which
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67 | is best for you.
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68 |
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69 | =over 4
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70 |
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71 | =item *
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72 |
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73 | If things aren't broken, upgrading perl may break
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74 | them (or at least issue new warnings).
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75 |
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76 | =item *
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77 |
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78 | The latest versions of perl have more bug fixes.
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79 |
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80 | =item *
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81 |
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82 | The Perl community is geared toward supporting the most
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83 | recent releases, so you'll have an easier time finding help for
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84 | those.
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85 |
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86 | =item *
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87 |
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88 | Versions prior to perl5.004 had serious security problems with
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89 | buffer overflows, and in some cases have CERT advisories (for
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90 | instance, http://www.cert.org/advisories/CA-1997-17.html ).
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91 |
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92 | =item *
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93 |
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94 | The latest versions are probably the least deployed and
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95 | widely tested, so you may want to wait a few months after their
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96 | release and see what problems others have if you are risk averse.
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97 |
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98 | =item *
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99 |
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100 | The immediate, previous releases (i.e. perl5.6.x ) are usually
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101 | maintained for a while, although not at the same level as the
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102 | current releases.
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103 |
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104 | =item *
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105 |
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106 | No one is actively supporting perl4.x. Five years ago it was
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107 | a dead camel carcass (according to this document). Now it's barely
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108 | a skeleton as its whitewashed bones have fractured or eroded.
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109 |
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110 | =item *
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111 |
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112 | There is no perl6.x for the next couple of years. Stay tuned,
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113 | but don't worry that you'll have to change major versions of Perl
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114 | soon (i.e. before 2006).
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115 |
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116 | =item *
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117 |
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118 | There are really two tracks of perl development: a
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119 | maintenance version and an experimental version. The
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120 | maintenance versions are stable, and have an even number
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121 | as the minor release (i.e. perl5.8.x, where 8 is the minor
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122 | release). The experimental versions may include features that
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123 | don't make it into the stable versions, and have an odd number
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124 | as the minor release (i.e. perl5.9.x, where 9 is the minor release).
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125 |
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126 | =back
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127 |
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128 |
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129 | =head2 What are perl4, perl5, or perl6?
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130 |
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131 | (contributed by brian d foy)
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132 |
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133 | In short, perl4 is the past, perl5 is the present, and perl6 is the
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134 | future.
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135 |
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136 | The number after perl (i.e. the 5 after perl5) is the major release
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137 | of the perl interpreter as well as the version of the language. Each
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138 | major version has significant differences that earlier versions cannot
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139 | support.
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140 |
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141 | The current major release of Perl is perl5, and was released in 1994.
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142 | It can run scripts from the previous major release, perl4 (March 1991),
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143 | but has significant differences. It introduced the concept of references,
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144 | complex data structures, and modules. The perl5 interpreter was a
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145 | complete re-write of the previous perl sources.
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146 |
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147 | Perl6 is the next major version of Perl, but it's still in development
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148 | in both its syntax and design. The work started in 2002 and is still
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149 | ongoing. Many of the most interesting features have shown up in the
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150 | latest versions of perl5, and some perl5 modules allow you to use some
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151 | perl6 syntax in your programs. You can learn more about perl6 at
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152 | http://dev.perl.org/perl6/ .
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153 |
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154 | See L<perlhist> for a history of Perl revisions.
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155 |
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156 | =head2 What is Ponie?
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157 |
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158 | At The O'Reilly Open Source Software Convention in 2003, Artur
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159 | Bergman, Fotango, and The Perl Foundation announced a project to
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160 | run perl5 on the Parrot virtual machine named Ponie. Ponie stands for
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161 | Perl On New Internal Engine. The Perl 5.10 language implementation
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162 | will be used for Ponie, and there will be no language level
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163 | differences between perl5 and ponie. Ponie is not a complete rewrite
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164 | of perl5.
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165 |
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166 | For more details, see http://www.poniecode.org/
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167 |
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168 | =head2 What is perl6?
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169 |
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170 | At The Second O'Reilly Open Source Software Convention, Larry Wall
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171 | announced Perl6 development would begin in earnest. Perl6 was an oft
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172 | used term for Chip Salzenberg's project to rewrite Perl in C++ named
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173 | Topaz. However, Topaz provided valuable insights to the next version
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174 | of Perl and its implementation, but was ultimately abandoned.
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175 |
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176 | If you want to learn more about Perl6, or have a desire to help in
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177 | the crusade to make Perl a better place then peruse the Perl6 developers
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178 | page at http://dev.perl.org/perl6/ and get involved.
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179 |
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180 | Perl6 is not scheduled for release yet, and Perl5 will still be supported
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181 | for quite awhile after its release. Do not wait for Perl6 to do whatever
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182 | you need to do.
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183 |
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184 | "We're really serious about reinventing everything that needs reinventing."
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185 | --Larry Wall
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186 |
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187 | =head2 How stable is Perl?
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188 |
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189 | Production releases, which incorporate bug fixes and new functionality,
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190 | are widely tested before release. Since the 5.000 release, we have
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191 | averaged only about one production release per year.
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192 |
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193 | Larry and the Perl development team occasionally make changes to the
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194 | internal core of the language, but all possible efforts are made toward
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195 | backward compatibility. While not quite all perl4 scripts run flawlessly
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196 | under perl5, an update to perl should nearly never invalidate a program
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197 | written for an earlier version of perl (barring accidental bug fixes
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198 | and the rare new keyword).
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199 |
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200 | =head2 Is Perl difficult to learn?
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201 |
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202 | No, Perl is easy to start learning--and easy to keep learning. It looks
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203 | like most programming languages you're likely to have experience
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204 | with, so if you've ever written a C program, an awk script, a shell
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205 | script, or even a BASIC program, you're already partway there.
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206 |
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207 | Most tasks only require a small subset of the Perl language. One of
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208 | the guiding mottos for Perl development is "there's more than one way
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209 | to do it" (TMTOWTDI, sometimes pronounced "tim toady"). Perl's
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210 | learning curve is therefore shallow (easy to learn) and long (there's
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211 | a whole lot you can do if you really want).
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212 |
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213 | Finally, because Perl is frequently (but not always, and certainly not by
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214 | definition) an interpreted language, you can write your programs and test
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215 | them without an intermediate compilation step, allowing you to experiment
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216 | and test/debug quickly and easily. This ease of experimentation flattens
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217 | the learning curve even more.
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218 |
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219 | Things that make Perl easier to learn: Unix experience, almost any kind
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220 | of programming experience, an understanding of regular expressions, and
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221 | the ability to understand other people's code. If there's something you
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222 | need to do, then it's probably already been done, and a working example is
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223 | usually available for free. Don't forget the new perl modules, either.
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224 | They're discussed in Part 3 of this FAQ, along with CPAN, which is
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225 | discussed in Part 2.
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226 |
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227 | =head2 How does Perl compare with other languages like Java, Python, REXX, Scheme, or Tcl?
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228 |
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229 | Favorably in some areas, unfavorably in others. Precisely which areas
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230 | are good and bad is often a personal choice, so asking this question
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231 | on Usenet runs a strong risk of starting an unproductive Holy War.
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232 |
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233 | Probably the best thing to do is try to write equivalent code to do a
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234 | set of tasks. These languages have their own newsgroups in which you
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235 | can learn about (but hopefully not argue about) them.
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236 |
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237 | Some comparison documents can be found at http://www.perl.com/doc/FMTEYEWTK/versus/
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238 | if you really can't stop yourself.
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239 |
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240 | =head2 Can I do [task] in Perl?
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241 |
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242 | Perl is flexible and extensible enough for you to use on virtually any
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243 | task, from one-line file-processing tasks to large, elaborate systems.
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244 | For many people, Perl serves as a great replacement for shell scripting.
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245 | For others, it serves as a convenient, high-level replacement for most of
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246 | what they'd program in low-level languages like C or C++. It's ultimately
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247 | up to you (and possibly your management) which tasks you'll use Perl
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248 | for and which you won't.
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249 |
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250 | If you have a library that provides an API, you can make any component
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251 | of it available as just another Perl function or variable using a Perl
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252 | extension written in C or C++ and dynamically linked into your main
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253 | perl interpreter. You can also go the other direction, and write your
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254 | main program in C or C++, and then link in some Perl code on the fly,
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255 | to create a powerful application. See L<perlembed>.
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256 |
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257 | That said, there will always be small, focused, special-purpose
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258 | languages dedicated to a specific problem domain that are simply more
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259 | convenient for certain kinds of problems. Perl tries to be all things
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260 | to all people, but nothing special to anyone. Examples of specialized
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261 | languages that come to mind include prolog and matlab.
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262 |
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263 | =head2 When shouldn't I program in Perl?
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264 |
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265 | When your manager forbids it--but do consider replacing them :-).
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266 |
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267 | Actually, one good reason is when you already have an existing
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268 | application written in another language that's all done (and done
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269 | well), or you have an application language specifically designed for a
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270 | certain task (e.g. prolog, make).
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271 |
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272 | For various reasons, Perl is probably not well-suited for real-time
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273 | embedded systems, low-level operating systems development work like
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274 | device drivers or context-switching code, complex multi-threaded
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275 | shared-memory applications, or extremely large applications. You'll
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276 | notice that perl is not itself written in Perl.
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277 |
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278 | The new, native-code compiler for Perl may eventually reduce the
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279 | limitations given in the previous statement to some degree, but understand
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280 | that Perl remains fundamentally a dynamically typed language, not
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281 | a statically typed one. You certainly won't be chastised if you don't
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282 | trust nuclear-plant or brain-surgery monitoring code to it. And Larry
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283 | will sleep easier, too--Wall Street programs not withstanding. :-)
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284 |
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285 | =head2 What's the difference between "perl" and "Perl"?
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286 |
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287 | One bit. Oh, you weren't talking ASCII? :-) Larry now uses "Perl" to
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288 | signify the language proper and "perl" the implementation of it,
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289 | i.e. the current interpreter. Hence Tom's quip that "Nothing but perl
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290 | can parse Perl." You may or may not choose to follow this usage. For
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291 | example, parallelism means "awk and perl" and "Python and Perl" look
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292 | OK, while "awk and Perl" and "Python and perl" do not. But never
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293 | write "PERL", because perl is not an acronym, apocryphal
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294 | folklore and post-facto expansions notwithstanding.
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295 |
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296 | =head2 Is it a Perl program or a Perl script?
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297 |
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298 | Larry doesn't really care. He says (half in jest) that "a script is
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299 | what you give the actors. A program is what you give the audience."
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300 |
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301 | Originally, a script was a canned sequence of normally interactive
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302 | commands--that is, a chat script. Something like a UUCP or PPP chat
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303 | script or an expect script fits the bill nicely, as do configuration
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304 | scripts run by a program at its start up, such F<.cshrc> or F<.ircrc>,
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305 | for example. Chat scripts were just drivers for existing programs,
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306 | not stand-alone programs in their own right.
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307 |
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308 | A computer scientist will correctly explain that all programs are
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309 | interpreted and that the only question is at what level. But if you
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310 | ask this question of someone who isn't a computer scientist, they might
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311 | tell you that a I<program> has been compiled to physical machine code
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312 | once and can then be run multiple times, whereas a I<script> must be
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313 | translated by a program each time it's used.
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314 |
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315 | Perl programs are (usually) neither strictly compiled nor strictly
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316 | interpreted. They can be compiled to a byte-code form (something of a
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317 | Perl virtual machine) or to completely different languages, like C or
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318 | assembly language. You can't tell just by looking at it whether the
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319 | source is destined for a pure interpreter, a parse-tree interpreter,
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320 | a byte-code interpreter, or a native-code compiler, so it's hard to give
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321 | a definitive answer here.
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322 |
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323 | Now that "script" and "scripting" are terms that have been seized by
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324 | unscrupulous or unknowing marketeers for their own nefarious purposes,
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325 | they have begun to take on strange and often pejorative meanings,
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326 | like "non serious" or "not real programming". Consequently, some Perl
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327 | programmers prefer to avoid them altogether.
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328 |
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329 | =head2 What is a JAPH?
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330 |
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331 | These are the "just another perl hacker" signatures that some people
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332 | sign their postings with. Randal Schwartz made these famous. About
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333 | 100 of the earlier ones are available from
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334 | http://www.cpan.org/misc/japh .
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335 |
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336 | =head2 Where can I get a list of Larry Wall witticisms?
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337 |
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338 | Over a hundred quips by Larry, from postings of his or source code,
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339 | can be found at http://www.cpan.org/misc/lwall-quotes.txt.gz .
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340 |
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341 | =head2 How can I convince my sysadmin/supervisor/employees to use version 5/5.6.1/Perl instead of some other language?
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342 |
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343 | If your manager or employees are wary of unsupported software, or
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344 | software which doesn't officially ship with your operating system, you
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345 | might try to appeal to their self-interest. If programmers can be
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346 | more productive using and utilizing Perl constructs, functionality,
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347 | simplicity, and power, then the typical manager/supervisor/employee
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348 | may be persuaded. Regarding using Perl in general, it's also
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349 | sometimes helpful to point out that delivery times may be reduced
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350 | using Perl compared to other languages.
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351 |
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352 | If you have a project which has a bottleneck, especially in terms of
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353 | translation or testing, Perl almost certainly will provide a viable,
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354 | quick solution. In conjunction with any persuasion effort, you
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355 | should not fail to point out that Perl is used, quite extensively, and
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356 | with extremely reliable and valuable results, at many large computer
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357 | software and hardware companies throughout the world. In fact,
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358 | many Unix vendors now ship Perl by default. Support is usually
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359 | just a news-posting away, if you can't find the answer in the
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360 | I<comprehensive> documentation, including this FAQ.
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361 |
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362 | See http://www.perl.org/advocacy/ for more information.
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363 |
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364 | If you face reluctance to upgrading from an older version of perl,
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365 | then point out that version 4 is utterly unmaintained and unsupported
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366 | by the Perl Development Team. Another big sell for Perl5 is the large
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367 | number of modules and extensions which greatly reduce development time
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368 | for any given task. Also mention that the difference between version
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369 | 4 and version 5 of Perl is like the difference between awk and C++.
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370 | (Well, OK, maybe it's not quite that distinct, but you get the idea.)
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371 | If you want support and a reasonable guarantee that what you're
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372 | developing will continue to work in the future, then you have to run
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373 | the supported version. As of December 2003 that means running either
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374 | 5.8.2 (released in November 2003), or one of the older releases like
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375 | 5.6.2 (also released in November 2003; a maintenance release to let perl
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376 | 5.6 compile on newer systems as 5.6.1 was released in April 2001) or
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377 | 5.005_03 (released in March 1999),
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378 | although 5.004_05 isn't that bad if you B<absolutely> need such an old
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379 | version (released in April 1999) for stability reasons.
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380 | Anything older than 5.004_05 shouldn't be used.
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381 |
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382 | Of particular note is the massive bug hunt for buffer overflow
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383 | problems that went into the 5.004 release. All releases prior to
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384 | that, including perl4, are considered insecure and should be upgraded
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385 | as soon as possible.
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386 |
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387 | In August 2000 in all Linux distributions a new security problem was
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388 | found in the optional 'suidperl' (not built or installed by default)
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389 | in all the Perl branches 5.6, 5.005, and 5.004, see
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390 | http://www.cpan.org/src/5.0/sperl-2000-08-05/
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391 | Perl maintenance releases 5.6.1 and 5.8.0 have this security hole closed.
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392 | Most, if not all, Linux distribution have patches for this
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393 | vulnerability available, see http://www.linuxsecurity.com/advisories/ ,
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394 | but the most recommendable way is to upgrade to at least Perl 5.6.1.
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395 |
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396 | =head1 AUTHOR AND COPYRIGHT
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397 |
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398 | Copyright (c) 1997-2006 Tom Christiansen, Nathan Torkington, and
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399 | other authors as noted. All rights reserved.
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400 |
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401 | This documentation is free; you can redistribute it and/or modify it
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402 | under the same terms as Perl itself.
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403 |
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404 | Irrespective of its distribution, all code examples here are in the public
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405 | domain. You are permitted and encouraged to use this code and any
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406 | derivatives thereof in your own programs for fun or for profit as you
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407 | see fit. A simple comment in the code giving credit to the FAQ would
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408 | be courteous but is not required.
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